fixodent,and forget it. Tonight here, video of a group of sightseers on vacation in los angeles that got more than they expected as they were driven past justin tim dberlake's mansion g. Suddenly chaos but not a real emergency. A prank. And tonight abc's clayton sandell says authorities are furious and saying at some point it could put someone in danger. Reporter: The calls sound frighteningly real. I shot my wife. You just shot your wife? Reporter: This part of a prank known as swatting is fake. Callers use so-called spoofing software to disguise their real phone number. Duping 911 operators and sending s.W.A.T. Teams racing to crimes that don't exist. Residents that we're responding, they may not have any idea that we're responding to their home. It could be scary. Reporter: And expensive. A fake call costs real money, about $10,000 each time. Celebrities are frequent targets, just this week, rihanna and p. Diddy and yesterday police showed up at the homes of selena gomez and justin timberlake. A call that four men entered the home and a call of someone being shot inside the home. It's very, very popular in los angeles. Reporter: Swatting takes advantage of outdated computer systems, tricking them into thinking a caller is in one location when they could be hundreds of miles away. When the police pull up caller i.D. And see a 310 number they have to track it back through the phone carrier and figure out where the call actually came from. Reporter: Newer technology may be able to stop them once and for all, including upgraded systems that use gps to identify where a call is really coming from. I'm going to shoot someone else soon. Reporter: So officers know if that emergency is for real or phony. Clayton sandell, abc news. Thank you.

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